It is known from GB-2240494A to provide dispensing apparatus in which a perforate membrane is vibrated such that liquid in contact with a rear face of the membrane is dispensed from a front face of the membrane as an atomised mist or spray. It is proposed that in the disclosed apparatus a predetermined dose is delivered by operation of a control circuit which regulates the dispensing period during which the membrane is vibrated, the supply of liquid being contained in a chamber of which the membrane constitutes a front wall.
A disadvantage of such an arrangement is that when not in use the liquid within the chamber is open to air through holes in the perforate membrane and may thereby be subject to evaporative losses or become bacteriologically contaminated or otherwise degraded.
A further disadvantage of such an arrangement is that variation in the rate at which liquid is dispensed through the membrane as a mist will result in variation in the total quantity delivered during the dispensing period.